1. Field of the Invention
The present invention relates to a photometric apparatus capable of multi-segmented photometry and more particularly to a photometric element for performing photometry when receiving object light reflected at the film surface or the shutter blind surface.
The present invention also relates to a photometric apparatus used in a TTL automatic light adjusting camera, and more particularly to that used in a camera having a focal plane shutter and an automatic light adjusting unit to be used at the time of photographing using a flash.
The present invention furthermore relates to a photometric apparatus in a camera having a light emission control unit.
2. Related Background Art
A photometric apparatus capable of so-called multisegmented photometry has been known in which the image plane is divided into a plurality of photometric regions and photometry is effected for each of the photometric regions. In this type of photometric apparatus, a plurality of photometric elements are arranged in a mirror box correspondingly to the photometric regions, and photomerry is performed by directing, respectively for each photometric region, the object light reflected at the shutter surface after passing through the photographing lens to said plurality of photometric elements via the photometric lens. Also, as a light adjusting device of an electronic flash unit, a device has been known in which the object light after passing through the photographing lens is caused to be reflected at a film surface, and light adjusting is performed by similarly directing the reflected light to a plurality of photoelectric elements, respectively, via the photometric lens.
In this specification, the term "photometry" is used to also signify the light adjusting in this type of electronic flash device.
There are however problems, as will be described below, in the conventional photometric apparatus because of the fact that a plurality of photometric elements are concentrated around a single point and that only a single photometric lens is provided.
FIG. 1 show the positional relationship, in a light adjusting device as described above, seen from the top of a camera, among a photometric lens 1, a photometric element 2 (a plurality photometric elements densely arranged around a single point) and film surface FI. In this figure, l1 denotes light entering from photometric regions, being incident upon the film surface, l2 denotes a regularly reflected light of the incident light l1, and l3 denotes dispersedly reflected light which is actually incident on the photometric element 2. In this case, the angle between the reflected light l3 and the regularly reflected light l2 (hereinafter referred to as diffusion angle) .theta. is rather large, to be .theta.1. In general, the smaller the diffusion angle .theta., the more intensified is the light incident on the photometric element 2, and, when the diffusion angle .theta. is large such as .theta.1, the amount of light received by the photometric element 2 is reduced because of the weakness of the light intensity of the reflected light l3. When these luminous quantities are less than the detectable limit of the photometric element 2, photometry becomes impossible.
Although the above described problem may be solved by increasing the diameter of the photometric lens 1 so as to increase the amount of light to be received, an increase in the size of the camera becomes unavoidable.
Furthermore, in FIG. 2 which describes conventional light adjusting operation, at the time of picture taking with a flash by using an electronic flash device (not shown), the luminous flux reflected from the object body is reflected at the film surface FI after passing the photographing lens LE, and the light due to the diffused reflection is directed to the photometric element 2 of the photoelectric conversion type through the photometric lens 1.
This photometric element 2 includes a main body 3, light receiving portion (not shown) fixed to the body 3 and a plurality of lead frames 4 extended from the body 3, and the body 3 is arranged with an inclination to the film surface FI. Thus the irregularly reflected light is received by the light receiving portion 5 after passing through the photometric lens 1, and a circuit portion (not shown) in the body 3 generates an electrical signal in accordance with the amount of the received light which is input into a light adjusting circuit, not shown, through the lead frames 4. The light adjusting circuit integrates the input current and, when the integrated amount reaches a predetermined amount, outputs a light emission stop signal so as to stop the light emission of the electronic flash device.
However, when an object with a high reflection rate, such as a gold-leafed folding screen, exists behind the subject (person) at the time of photographing using a flash, because of the fact that the light adjusting is effected on the basis of the reflected light, it may result in a photograph of so-called "under exposure" where the face of a person, the main subject, is darkened all over. In accordance with one aspect of the present invention, for the purpose of obtaining an appropriate exposure at any photographing condition at the time of photographing with a flash, in the specification of Japanese Patent Application No. 1-204300 in which the film surface FI is segmented for example into five regions 6a.about.6e as shown in FIG. 3 and the reflected light from each region is received by each of separate light receiving portions 7a.about.7e so that the light adjusting is effected on the basis of the results of light reception at respective portions.
Referring to FIG. 3, in other words, the lights reflected from the regions 6a, 6b of the regions of the film surface FI are respectively received by light receiving portions 7a, 7b, through a photometric lens 8c, while the reflected light from the region 6c is received by a light receiving portion 7c through a photometric lens 8b. Furthermore, the reflected lights from the regions 6d, 6e are received by light receiving portions 7d,7e through a photometric lens 8a.
It should be noted that the term "photometry" in this specification is used to refer to both the so-called ordinary photometry for the exposure control and light adjusting of an electronic flash device as described above.
In the case of using a photometric element as above, however, a certain distance or more is necessary between the photometric lens and the light receiving portion to obtain a conjugate relationship between the light receiving portion and the film surface FI. In addition, the integration of the light receiving portion and the circuit portion, for the purpose of improving the light adjusting precision, results in an enlargement of the element and an increase in the number of lead frames, which can lead to a disadvantage that the camera will be increased in size because of the increase in the arrangement space for the photometric element in the camera body. In particular, the above mentioned problem is more serious in nature when employing the segmented photometric (light adjusting) system as described above, because the photometric element itself must be enlarged due to an increase in the number of the light receiving portions.
Further, because of the increasing availability of auto-focus (AF) systems of a camera in the recent years, an AF sensor module is more likely to be placed at the bottom of a camera body. From the viewpoint of the coexistence of such AF sensor module and the above described photometric element, the increase in the space for the disposition of the above described photometric element becomes even more disadvantageous.
Conventionally, furthermore, a TTL auto light adjusting control device used for the flash photographing of a camera having a focal plane shutter is provided with a single light receiving element at a position from which a portion or the whole of film surface can be supervised, and the flash apparatus is caused to emit light after fully opening the shutter. Thus, by effecting a photoelectric transfer of the light due to the reflection of an image in the object field at the film surface and by comparing the signal corresponding to the integrated amount of the light with a predetermined amount of light, the amount of light to be emitted from the flash apparatus is controlled so as to secure a certain luminosity at the film surface.
Moreover, it is also known to construct a photometric means for steady light in such a manner that the photometry is effected by segmenting the object field into a plurality of regions so as to previously detect the state of the object under the steady light level, and a correction on the basis of the result is made with respect to the light amount level to be controlled at the time of a flash photographing.
Since, however, the conventional art controls the emitted light amount from a flash apparatus as an average within a predetermined region of the film surface which is looked over by the light receiving element at the time of the light adjustment for flash photographing to obtain a certain exposure level, a wide variance in the resulting pictures is caused depending on the condition of the object. When for example a flash photographing is effected, for a main object which occupies only a small portion of the image field and which is located on a deeply spaced background, by a camera in which the range supervised by the light receiving element is the entire film surface, the light emission quantity accordingly controlled has an effect of an over-exposure for the main object because there is a wide portion at which the light from the flash apparatus is not reflected.
On the other hand, when using a camera in which the range supervised by the light receiving element is a center portion of the film surface, the exposure for the main subject may be erroneous if a flash photographing is effected under a condition where the main object is out of the center portion and the center portion is occupied by an object which is located at a distance different from that of the main object.
Furthermore, when the configuration is such that the light emission level to be controlled at the time of a flash photographing is corrected on the basis of the condition of the object which is previously detected under a steady light level with the photometry using photometric means for steady light by segmenting the object field into a plurality of regions, an appropriate correction is not likely to be effected because of the fundamental difference between the object image under steady light and the object image under flash light. In an extreme case, for example, necessary information is hardly obtained for the night-time photographing with the steady light photometry and the light adjusting are after all without any correction, whereby the above described problems remain unsolved.
As one of the proposals to eliminate the problems as above, Japanese Patent Laid-Open No. 60-15626 has been provided. This discloses a camera incorporating a stroboscope of the so-called externally light-adjusted type. In this configuration, the image field is divided into two regions, the center portion and the peripheral portion, to detect the difference in the output of these two regions by a preliminary flash, and, on the basis of the amount of such difference, one with a larger output is determined to be the main object if the difference exceeds a predetermined amount so that only the center or only the periphery is almost exclusively subjected to the light adjusting for the main flash at the time of photographing, while both are subjected to the light adjusting on an average basis if the difference is less than the predetermined value. Thus, "the stroboscope light is controlled so that an appropriate exposure is achieved at all times by eliminating the influence due to the difference in the composition of the scene to be photographed" and in an embodiment, a detection system for the object field using a preliminary flash and a detection system for the light adjustment control at the time of main flash are provided as separate systems from the photographing optical system.
However, in a system according to the above described conventional example, of the two regions divided at the time of preliminary flash, the region with larger output is always decided to be the region at which the main object is located. Therefore, when for example a gold-leafed folding screen is placed right behind the subject person, the output is larger for the region without the subject person, and, if the stroboscope light is adjusted by emphatically effecting photometry for this region at the time of main flash, a photograph will result where the subject person is underexposed. In other words, the above described invention is not only incapable of solving the conventional problems due to the difference in the reflectivity of the object body but also with such a disadvantage that the stroboscope may be controlled reversely, to a wrong direction.
Furthermore, since the detection systems in the disclosed example of the above described invention are of the type externally adjusting the light, it cannot be employed in a camera of which lenses are changeable, because the segmenting configuration of the object field in the detection system and the segmenting configuration of the object field on the film surface are changed depending on the type of lenses due to difference in the image angle.
Still furthermore, FIG. 4 shows the configuration of a conventionally known TTL auto light adjusting camera. The condition at the time of observation through the finder is such that the luminous flux (steady light) after passing through the photographing lens LE of a single-lens reflex camera is reflected by a mirror 10 at its mirror-down state as shown by the broken line and a portion of which is directed to an eye-lens 13 via a screen 11 and a pentagonal prism 12 while another portion of which is directed to an exposure calculating photometric element 15 via a photometric lens 14. And the condition of the camera at the time of photographing is such that, when for example a flash photographing is to be effected at an adverse light condition under a clear sky, both the steady light and the light emitted from a flash apparatus 16 and reflected by the object body pass through the photographing lens LE and reach the film surface FI through an opened shutter 17 because the mirror 10 is retracted to the position as shown by a solid line. The light reflected at the film surface FI is directed to a light adjusting photometric element 7 via a photometric lens 8.
In this configuration, the photometric output of the exposure calculating photometric element 15 is used in determining the exposure value. Further, the photometric output of the light adjusting photometric element 7 is used in determining the timing for stopping the emission of the flash apparatus 16. In other words, the emission is stopped when the integrated value of the output of the light adjusting photometry reaches a predetermined light amount.
In such a conventional TTL auto light adjusting camera, the emission amount may be affected depending on the percentage of the image field occupied by the main object (such as persons) or existence/nonexistence of a highly reflective object such as a gold-leafed folding screen, and the light adjusting may not be properly effected. Thus as proposed in the specification of commonly assigned Japanese Patent Laid-open No. 2-87127 photometry is effected by segmenting a light adjusting photometric element 7 into a plurality of regions; the reflectivity distribution (luminance distribution) of the object field is obtained from the photometric output of the light adjusting photometric element 7 by executing a preliminary flash prior to the main flash, and the output for each photometric region is corrected by weighting in accordance with such reflectivity distribution to accurately adjust the light.
However, since such a TTL auto light adjusting camera is designed to perform a preliminary flashing for any flash photographing regardless of the set aperture value so as to effect a correction by means of weighting, an appropriate light adjusting may not be achieved at the time of using a small aperture value because the photometry by the light adjusting photometric element 7 based on the preliminary flashing cannot be accurately performed due to an insufficiency of light.
Still furthermore, when using a conventional camera such as described above in the dark such as during a night, the following problems arise, for example when the main object is a person, even if such as the image angle of the photographing angle and the distance to the main object are the same. Specifically, in cases:
(1) where the percentage of the image plane occupied by the persons is different due such as to a difference in the number of persons or a difference in the image composition; PA1 (2) where in a room there is a difference in the distance from the person to the,background wall; PA1 (3) where a hollowness-like state occurs or the background condition differs when there is a wall at the background or when the background is such as a landscape; or PA1 (4) where a difference occurs due to existence/nonexistence of a highly reflective portion such as a wedding cake or a gold-leafed folding screen;
there has been a problem that a difference in the emission amount occurs at the time of TTL light adjusting control due to such differences in the condition.
Further in the case such as during the daytime where it is well-lighted, if a TTL light adjusting is effected by using the photometric element 7 when an extremely bright object such as the sun enters in a portion of the image plane, there has been a problem such that an underexposure of the main object occurs because of insufficiency of light provided by the flash apparatus 16.
This is because the TTL light adjusting system is based on the principle that the steady light and the light, emitted from the flash apparatus 16, returning as the result of reflection at the object body are at the same time indiscriminately subjected to the photometry so as to stop the emission of the flashing means upon the detection of the fact that such amount has reached a predetermined amount. Thus, if a highly bright object occupies a portion of the image plane so as to increase the steady light component, the amount to be emitted by the flash apparatus is accordingly controlled to a smaller amount.